Snowmobile rear suspension

ABSTRACT

A snowmobile rear suspension is shown comprised of a linear force element (LFE) positioned outside the envelope of the snowmobile endless track. The LFE is attached at one end to the frame and at the other end to a bell crank. The bell crank is operatively connected to the slide rails. When the slide rails collapse in normal operation, the bell crank strokes the LFE, and the suspension is progressive throughout the range.

This application claims priority from provisional patent applicationSer. No. 60/776,467 filed Feb. 24, 2006, the disclosure of which isfully incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to suspension systems for snowmobiles, andmore particularly, the present invention relates to snowmobile rearsuspensions. In an illustrated embodiment, progressive rate rearsuspension architecture for snowmobiles is disclosed.

Performance characteristics of snowmobiles, including the comfort of theride, depend on a variety of systems and components, including thesnowmobile suspension. Typically, a snowmobile suspension includes twosystems, a front suspension system for a pair of skis and a rearsuspension system for the track.

The rear suspension of a snowmobile supports an endless track driven bythe snowmobile engine to propel the machine. The track is supportedbeneath a vehicle chassis by a suspension that is designed to provide acomfortable ride and to help absorb the shock of the snowmobile crossinguneven terrain. Most modern snowmobiles use a slide rail suspensionwhich incorporates a pair of slide rails along with several idler wheelsto support the track in its configuration. The slide rails are typicallysuspended beneath the chassis by a pair of suspension arms, with eacharm being attached at its upper end to the chassis of the snowmobile,and at its lower end to the slide rails. The mechanical linkage of theslide rails to the suspension arms and to the snowmobile chassistypically is provided by springs and at least one element acting along alinear path, such as a shock absorber, damper, air shock, shock andspring combination, or other linear force element (LFE). The springs areloaded to bias the slide rails downwardly away from the snowmobilechassis and the shock absorbers; dampers or LFEs provide damping forcesfor ride comfort.

There are presently two general types of snowmobile rear suspensions inall of the snowmobile industry: coupled and uncoupled. The term“coupled” is given to suspensions that have dependant kinematicsfront-to-rear and/or rear-to-front (relative to the rear suspension railbeam). That is, a suspension is coupled “front-to-rear” when the frontof the suspension is deflected vertically and the rear also movesvertically to some degree. A suspension is coupled “rear-to-front” whenthe rear of the suspension is deflected vertically and the front alsomoves vertically to some degree. A suspension is considered to becoupled “tighter” front-to-rear, or increased coupling bias to thefront, if a front deflection causes near the same rear deflection. Thesame is true if a suspension is coupled “tighter” rear-to-front, orincreased coupling bias to the rear: a rear deflection causes near thesame front deflection. An uncoupled rear suspension functionsindependently front-to-rear and rear-to-front. A deflection of the frontportion of the suspension causes little to no deflection of the rearportion and vice versa.

There are two main advantages to a coupled suspension. First, a coupledsuspension shares rate when coupled. There is a distinct rate associatedwith the front of the suspension and a separate distinct rate associatedwith the rear of the suspension; when a suspension “couples” it borrowsthe rate of both the front and rear of the suspension so the overallrate becomes higher than could have been achieved without coupling.Second, coupling is used to control weight transfer during acceleration.An uncoupled suspension will allow excessive chassis pitch due to theindependence of the suspension. Coupling stops this by limiting theangle of the slide rail and by increasing the rate of the suspension and“locking” the suspension geometry.

Typically the use of a coupled suspension, uncoupled suspension, and thedegree to which a suspension is coupled depends on the expected use.Coupled suspensions are mostly used on trail/performance snowmobileswhere large bumps and tight corners require increased rate andcontrollable weight transfer. Uncoupled suspensions are used on deepsnow/long track snowmobiles where weight transfer and traction are moreimportant.

There are many ways to create a coupled rear suspension. The simplestform of a rear suspension is a four-link suspension created by thechassis, two arms, and the slide rails all connected with rotationalpivots. This type of suspension yields only one degree of freedom. Theslide rail motion and suspension kinematics are predefined by the lengthof the 4 links and cannot be altered due to the location of the input(front, rear, or between). This is not desirable because the slide railwill not follow undulating terrain or allow any angle change relative tothe chassis due to acceleration. To fix this problem with a basicfour-link, one of the links is allowed to change length to some degree.The geometry of the four-link therefore changes relative to the locationof the input. A deflection of the front portion of the suspension yieldsone distinct four-link geometry and a deflection of the rear portion ofthe suspension yields different distinct four-link geometry. There isalways some degree of uncoupled behavior in a coupled suspension whenthe geometry is not locked front-to-rear or rear-to-front. It isimportant to note that most coupling is focused on rear-to-front to helpcontrol excessive weight transfer. The majority of differences in rearsuspension architecture are driven by accomplishing this same goal of a“sloppy” four-link in different ways.

FIG. 1 illustrates an example of a traditional rear suspension 10(illustratively a 2D model of the Polaris Fusion® snowmobile rearsuspension design) having slide rails 12, a front suspension arm 14 anda rear suspension arm 16. Front suspension arm 14 is coupled to theslide rails 12 by pivot connection 18. An opposite end of frontsuspension arm 14 is pivotably coupled to the chassis. Rear suspensionarm 16 is pivotably coupled to the slide rails 12 by pivot connection20. An opposite end of the rear suspension arm 16 is pivotably coupledto the chassis. Torsion springs are illustratively mounted between therear torque arm and slide rails 12. First and second linear forceelements (LFE) 22 and 24 are coupled between the first and secondsuspension arms 14 and 16, respectively and the slide rails 12 in aconventional manner.

FIG. 1 labels the following geometry of a four bar link which is similarin most snowmobile rear suspensions as illustrated by the linesdefining: A) Front Link, B) Rear Link, C) Rail Link, and D) ChassisLink. These links and their relative lengths govern the majority of rearsuspension kinematics.

The coupling bias behavior as described above is dependant on thisfour-link geometry and is important to rear suspension rate, impactharshness, and ride quality. For example, a perfectly symmetricfour-link (A=B and C=D, A parallel to B and C parallel to D) will yielda rail angle that is maintained at the same angle throughout travel. Inother words, the rail 12 does not rotate relative to the chassis as thesuspension is compressed. This type of movement is not desirable due tothe need to achieve traction on undulating terrain. As deviations tothis symmetric geometry are made, the rail angle will change throughoutsuspension travel.

As traditional suspensions are compressed, the front arm begins to“point” at the rear arm mount location. This is known as “overcentering”. FIGS. 2 and 3 illustrate this graphically, showing how linksA and C have become substantially a straight line.

A rear suspension that is coupled rear-to-front has the sameover-centering problems as discussed above for a front load situation,but to a larger degree. FIG. 4 illustrates this problem graphically whena rear load is applied as illustrated by arrow 27, showing how link Bhas crossed over link C. As mentioned above, over-centering drasticallyreduces effective suspension rate and damper velocities.

The problem lies in packaging a four link geometry that does not moveover-center during compression. Consider another common four-linksuspension, the SLA (Short-Long Arm) suspension. FIG. 5 illustrates acommon snowmobile SLA front suspension 30 with labels equivalent to FIG.1 for links A, B, C and D. Details of the SLA front suspension aredescribed in U.S. Pat. No. 6,942,050 which is incorporated herein byreference. This arrangement does not move over-center upon compressiondue the placement of chassis mount points of A and B at locations 17 and19, respectively, in FIG. 5. The vertical separation is a highpercentage of link D. Therefore, the first factor in eliminatingover-centering in rear suspensions is to place the rear armsignificantly higher than the front arm as outlined in the abovediscussion about coupling behavior.

Simply moving the rear point of a conventional suspension upward is notfeasible. The rear arm needs to become significantly shorter than thefront. Typical link ratios (A/B) on conventional suspensions are between1 to 1.5. Ratios other than this are not feasible or do not package incurrent design envelopes. However, to accommodate a higher rear mount,A/B ratios need to increase to the range of about 1.6 to 2.0. Therefore,in an illustrated embodiment, A/B ratios are preferably 1.6 to 2.0 orgreater in coupled suspensions. FIG. 6 illustrates the difference in arear load case coupling angle between a conventional suspension labeledas “Prior Art” (illustratively the Polaris IQ 440 suspension) and theillustrated embodiment described below (labeled as “Improved RearSuspension Coupled” and “Improved Rear Suspension Uncoupled”).

FIG. 7 illustrates the difference in the coupling angle between aconventional suspension and the suspension of the present improvedsuspension invention described below. Conventional suspensions yield afront coupling angle that increases through travel. This means that asthe conventional suspension is compressed, the angle of the slide railincreases. This type of behavior is not ideal because as the rail angleincreases, rate and damper velocities decrease ultimately resulting in aregressive suspension. More desirable is a rail angle that decreases asthe suspension is compressed; thus, effectively making the suspensionrate progressive (the more regressive the rail angle, the moreprogressive the rate). However, an increasing coupling angle isdifficult to eliminate due to the packaging of a traditional snowmobilesuspension. In the illustrated embodiment of the present invention,unconventional packaging of the suspension components results in avertical difference between the front arm and rear arm chassis mounts ofpreferably 20% or more of the chassis link length (D) which results in adecreasing coupling angle.

Further examination of coupling behavior yields two constraintsnecessary to maintain reasonable component loads and basic function ofthe rail/ground interface. First, this angle should be positive. Inother words, when a load is applied to the front of the suspension asillustrated by arrow 25 in FIG. 3, the front portion of the slide rails12 moves more than the rear portion and vice versa for a load applied tothe rear of the suspension. Second, there should be no inflections, orchange in sign of the slope, in the curve of rail angle versus verticaldeflection, as shown in FIGS. 6 and 7. In other words, when a load isapplied to the front of the suspension, at no point should the rear ofthe suspension begin to move faster than the front and vice versa for aload applied to the rear of the suspension.

Because an uncoupled suspension does not form a distinct four-link, noover-centering can occur. No link ratio is then necessary for a rearload case in an uncoupled suspension. This is very beneficial, butexcessive vehicle pitch and lack of vertical rate usually make uncoupledsuspensions behave poorly for load carrying capacity and ride quality.Typically, for these suspensions a link ratio is then tuned only for thefront load case. The shock/spring ratio can be tuned to help counteractthe deficiencies of an uncoupled suspension. In this way, the rear armgeometry is tuned exclusively to maximize rear load case rate.Therefore, linkage arm length ratios are tuned for front coupling andrear rate in uncoupled suspensions.

As discussed above, the majority of snowmobile rear suspensionarchitectures utilize a combination of springs, dampers, or othersimilar linear force elements (LFE), all packaged within the envelope ofthe track. Regardless of how these elements are packaged, these designstypically use two methods to generate vertical rate: 1) the LFE islocated so that there is some vertical component reacted between thesuspension arm and rail beam, and 2) the LFE is connected to thesuspension arm such that a torque reaction is generated about the upperpivot. The inherent problem is that these designs lose rate near fulljounce due to the suspension mechanism components becoming generallyplaner. That is, all the suspension components fold down until they arelying relatively flat as the suspension components move at full jounce.This is due to the large vertical travel requirements of a snowmobilesuspension.

The result of the suspension components becoming planar is that the loadvector of the LFEs begins to point horizontally instead of vertically.This transfers load into the internal components of the suspension anddoes not react vertically to suspend the vehicle. Also, as thesuspension components become planar, the moment arm through which thesuspension reacts increases at a faster rate than can be controlled bythe shock/spring ratio, regardless of the type of linkage used toaccelerate the shock/spring.

With reference again to FIGS. 1 and 2, FIG. 1 shows a 2D representationof suspension 10 at full rebound. FIG. 2 shows suspension 10 at fulljounce. The front and rear LFEs 22, 24 become generally planar and laydown and point nearly horizontally in FIG. 2. The rear torque arms get“longer” measured from the upper pivot to lower pivot in the horizontaldirection. Even with a complicated linkage to help stroke the rear LFE24, a progressive rate cannot be maintained due to the two reasonslisted above. This is true for all conventional snowmobile rearsuspension systems.

Load at the slide rails and, more importantly, the bias between frontand rear load is directly related to coupling, especially for a frontload case. Consider the traditional suspension as illustrated in FIG. 1.The architecture is such that the front spring/damper 22 acts betweenthe front arm 14 and the slide rail 12, and both the torsion springs andrear damper 24 act between the rear arm 16 and the slide rail 12 nearthe front. Therefore, during a front load case, both springs and dampers22, 24 have a large effect on load and rate. The same is true of a rearload case. Attempting to tune the front LFE 22 will change the load/rateat the front and rear, and vice versa. Also if the coupling wereincreased, the rail angle decreases through travel and the rate willincrease. In order to tune the suspension rate, the front LFE 22, rearLFE 24 and torsion springs, and coupling angle all need to be adjusted.

To improve this system: 1) Front coupling can be used primarily tocontrol front load/rate, 2) Front preload is adjusted by a small LFEnear the front of the rail (has a very small affect on rate), and 3)rear preload and rate is determined by the rear arm only. To achievethis with actual architecture, the main rear LFE needs to react only atthe rear arm and with no other suspension components. Therefore reactingthe LFE on the chassis in the above discussion is important not only forprogressive rate, but also for load bias. When these three conditionsare true, rear coupling does not greatly influence rate. This isrealized because the front LFE is only used for preload so there isgenerally very little rate to “borrow” from the front of the rail duringa rear load case.

Progressive rate suspensions have not yet been achieved in snowmobilerear suspension designs because 1) the vertical component of the LFEbecomes very small as the LFEs become horizontal and planar with thesuspension during jounce, and 2) the rotational component of the LFEabout the arm pivot also cannot increase faster than the increase in armlength moment.

The state of snowmobile rear suspensions in the industry consistsentirely of falling rate, or regressive suspension designs. Even thoughthere is a large variety in the suspension architecture from onemanufacture to another, commercially available designs yield an overallsuspension stiffness that decreases as the suspension is compressedtoward full jounce. Some architectures yield discontinuities that maylocally spike the rate for a short time (such as an overload spring),but afterwards the rate continues to decrease. Because most designeffort is directed at optimizing a damper or spring motion ratio insteadof analyzing the entire suspension system there are currently noprogressive rate suspensions in the industry.

Now with regard to chassis construction, traditional snowmobile chassisstructures consist of elements common to each manufacturer, especiallyin the tunnel and rear suspension portion of the snowmobile. Typically,the rear suspension includes two suspension arms attached to the chassistunnel frame and a drive shaft mounted forward of the front arm to drivethe endless track.

This conventional suspension arrangement poses two problems. First,track tension through suspension travel relies on the relative placementof the suspension arms and wheels to the drive shaft. Suspension mountlocations are often determined not only by specific, desired suspensioncharacteristics, but also on track tension packaging. Problems areencountered from both an over and under tensioning track standpoint.Second, the front arm placement is limited to remain outside the drivesprocket diameter due to interference with drive train components. Thiscreates problems when attempting to change the weight transfer behaviorof the rear suspension, which is dominated by front arm mount location.

Achieving the mount points for desirable rate and kinematics is onlyhalf the challenge of snowmobile suspension design. Packaging a trackaround the suspension is the other. Traditional suspensions sacrificemore optimum suspension geometry to provide track tensioning andpackaging which can be extremely difficult to manage.

All of these problems are solved by mounting the front swing arm coaxialwith the drive shaft as discussed below. Because the front swing armrotates around the same axis as the track drive sprocket, track tensionis only influenced by the slide rail approach bend profile and a rearsuspension idler pulley. Also, the coaxial placement of the arm createsimproved weight transfer behavior of the rear suspension.

In order to generate necessary traction under acceleration, weighttransfer and pitch need to be considered. Suspension parameters aretuned to facilitate the shift of vehicle weight from the skis to thetrack. This shift in weight is imperative for snowmobile accelerationdue to slippery ground conditions. There are many parameters, but thetwo that dominate are front arm mount locations and carrier wheel.

Vehicle pitch is partially a result of this weight shift, but excessivepitch can result without increased traction. Packaging constraints, suchas track carrier wheels, within the design of the suspension may limitor increase the ability of the vehicle to pitch.

With this design, the improved suspension may eliminate the carrierwheel. This changes the load vector into the suspension from the trackdue to tractive forces between the track and ground. In the illustratedembodiment, the load vector from the track is more horizontal whichinduces less pitch and weight transfer than a traditional suspension. Toimprove this, the front arm is moved significantly forward to facilitateweight transfer. This point can move forward incrementally until itencounters the drive wheel inscribed circle. At this point, it can onlymove coaxial with the drive sprocket. The illustrated embodiment of thepresent invention utilizes a coaxial front arm mount as discussed hereinto facilitate weight transfer and pitch.

As for the frame assemblies, traditional snowmobiles utilize a longtunnel structure to which the driveshaft and rear suspension mountsbeneath. Above the tunnel typically sits a fuel tank and seat. This typeof structure is adequate because most spring/damper forces are reactedinternal to the suspension and between the front and rear arm mounts.Additional structure to the base tunnel is only required between thesemounts.

SUMMARY OF THE INVENTION

The embodiments disclosed herein provide a snowmobile suspension system,comprising a frame; slide rails for mounting endless track; at least onelinkage between the slide rails and frame, the linkage comprising apivot link, where the pivot link pivots in response to movement betweenthe slide rails and the frame; and at least one linear force element(LFE) positioned between the pivot link and the frame, whereby pivotalmovement of the pivot link strokes the LFE.

The at least one LFE may be positioned above the frame. The at least oneLFE may be substantially horizontal throughout its movement. The atleast one linkage may be positioned adjacent to a rear of the sliderails and defines a rear suspension system. The pivot link may becomprised of a bell crank, which connects to one end of the LFE. Thelinkage may be further comprised of a rear suspension frame operativelylinked to the slide rails and the bell crank. The rear suspension framemay be comprised of straddle links, which flank the endless track. Thestraddle links may be defined as A-shaped links, having pluralattachments to the slide rails and a single upper pivot link. The bellcrank may be pyramidally shaped, with front corners attached to theframe, rear corners operatively connected to the slide rails, and theapex attached to the LFE.

In another embodiment, a snowmobile suspension system, comprises aframe; slide rails for mounting endless track; at least one linkagebetween the slide rails and frame; and at least one linear force element(LFE) positioned above the frame and operatively connected to the frameand to the at least one linkage.

The at least one linkage may be positioned adjacent to a rear of theslide rails and defines a rear suspension system. The linkage may becomprised of a bell crank, which connects to one end of the LFE. Thelinkage may be further comprised of a rear suspension frame operativelylinked to the slide rails and the bell crank. The rear suspension framemay be comprised of straddle links, which flank the endless track. Thestraddle links may be defined as A-shaped links, having pluralattachments to the slide rails and a single upper pivot link. The bellcrank may be pyramidally shaped, with front corners attached to theframe, rear corners operatively connected to the slide rails, and theapex attached to the LFE.

In yet another embodiment, a snowmobile suspension system, comprises aframe; slide rails for mounting endless track; at least one linkagebetween the slide rails and frame; and at least one linear force element(LFE) positioned substantially horizontally, with one end attached tothe frame and one end connected to the at least one linkage.

The at least LFE may be positioned above the frame. The at least one LFEmay be substantially horizontal throughout its movement. The linkage maybe comprised of a pivot link which pivots in response to movementbetween the slide rails and the frame, and LFE is positioned between thepivot link and the frame, whereby pivotal movement of the pivot linkstrokes the LFE. The at least one linkage may be positioned adjacent toa rear of the slide rails and defines a rear suspension system. Thepivot link may be comprised of a bell crank, which connects to one endof the LFE. The linkage may be comprised of a rear suspension frameoperatively linked to the slide rails and the bell crank. The rearsuspension frame may be comprised of straddle links, which flank theendless track. The straddle links may be defined as A-shaped links,having plural attachments to the slide rails and a single upper pivotlink. The bell crank may be pyramidally shaped, with front cornersattached to the frame, rear corners operatively connected to the sliderails, and the apex attached to the LFE.

In another embodiment, a snowmobile suspension system, comprises aframe; slide rails coupled to the frame; endless track mounted to theslide rail; at least one linear force element (LFE) positioned outsideof the envelope defined by the endless track; a suspension assemblycoupling the slide rails to the frame; whereby one end of the LFE isattached to the frame and the opposite end is attached to the suspensionassembly, with the endless track passing through the suspensionassembly.

The at least LFE may be positioned above the frame. The at least one LFEmay be substantially horizontal throughout its movement. The suspensionassembly may be comprised of a pivot link which pivots in response tomovement between the slide rails and the frame, and LFE is positionedbetween the pivot link and the frame, whereby pivotal movement of thepivot link strokes the LFE. The pivot link may be comprised of a bellcrank, which connects to one end of the LFE. The suspension assembly maybe comprised of straddle links, which flank the endless track. Thestraddle links may be defined as A-shaped links, having pluralattachments to the slide rails and a single upper pivot link. The bellcrank may be pyramidally shaped, with front corners attached to theframe, rear corners operatively connected to the slide rails, and theapex attached to the LFE.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present snowmobile will now be discussed withreference to the drawings, where:

FIG. 1 shows a diagrammatical view of a conventional snowmobilesuspension system in full rebound;

FIG. 2 shows a diagrammatical view of a conventional snowmobilesuspension system in full jounce;

FIG. 3 shows the diagrammatical view of a conventional snowmobilesuspension system according to FIG. 1 and 2, with a front load applied;

FIG. 4 shows the diagrammatical view of a conventional snowmobilesuspension system according to FIG. 1 and 2, with a rear load applied

FIG. 5 shows a diagrammatical view of a conventional snowmobile frontsuspension system;

FIG. 6 shows a comparison curve of the prior art versus the improvedsuspend with a rear load;

FIG. 7 shows a comparison curve of the prior art versus the improvedsuspend with a front load;

FIG. 8 shows a diagrammatical perspective view of the suspension of thepresent invention;

FIG. 9 shows a diagrammatical plan view of the suspension of FIG. 8;

FIG. 10 shows a diagrammatical plan view of the suspension of thepresent invention at full rebound;

FIG. 11 shows a diagrammatical plan view of the suspension of thepresent invention at full jounce;

FIG. 12 shows a diagrammatical perspective view of an alternatesuspension;

FIG. 13 shows a diagrammatical plan view of the suspension of thepresent invention retro-fit on an existing suspension;

FIG. 14 shows a diagrammatical plan view of another suspension of thepresent invention retro-fit on an existing suspension;

FIG. 15 shows a perspective view of the suspension of the presentinvention applied to a tunnel and to slide rails;

FIG. 16 shows a perspective view of the suspension of FIG. 16, with thechassis and tunnel removed;

FIG. 17 shows a plan view of the FIG. 16 embodiment;

FIG. 18 shows an enlarged perspective view of FIG. 16, showing the frontsuspension mounts;

FIG. 19 shows an enlarged view of the connection of the front suspensionmounts of FIG. 18 to the slide rails;

FIG. 20 shows a partial sectional view of one driveshaft assembly;

FIG. 21 shows the driveshaft assembly of FIG. 20, partiallydisassembled;

FIG. 22 shows a partial sectional view of another possible driveshaftassembly;

FIG. 23 shows the driveshaft assembly of FIG. 22, partiallydisassembled;

FIG. 24 shows an enlarged perspective view of FIG. 16, showing the rearsuspension mounts to the slide rails;

FIG. 25 shows an enlarged perspective view showing the pivotal slidingcoupling connection of the rear suspension mounts to the slide rails;

FIG. 26 shows an enlarged perspective view of the rear deflector shield;

FIG. 27 shows an enlarged perspective view of the rear chassis of FIG.15 removed;

FIG. 28 is a diagrammatical view shows the force vectors applied to thesuspension system;

FIG. 29 is a perspective view of an alternate rear chassis removed;

FIG. 30 shows the rear chassis of FIG. 29 attached to a tunnel;

FIG. 31 shows the rear chassis of FIG. 30 with a seat mounting frame;

FIG. 32 shows a seat bun mounted on the seat frame of FIG. 31;

FIG. 33 shows an alternate tunnel mounted seat frame;

FIG. 34 shows a seat bun mounted on the seat frame of FIG. 33;

FIG. 35 is a diagrammatical illustration of the four-link geometry ofthe embodiment of FIGS. 15-17;

FIG. 36 shows the diagrammatical view of FIG. 35 with front loadedcoupling;

FIG. 37 shows the diagrammatical view of FIG. 35 with rear loadedcoupling;

FIG. 38 shows a comparison load vs. deflection curve of the prior artversus the improved suspension with a front load;

FIG. 39 shows a comparison load vs. deflection curve of the prior artversus the improved suspension with a rear load;

FIG. 40 shows a comparison curve of regressive versus progressivesuspensions;

FIG. 41 shows progressive rates for three load cases;

FIGS. 42-44 are computer simulations of movement of the progressive rearsuspension of the present invention;

FIGS. 45-48 are plots characterizing the general behavior of thesuspension of the present invention, compared to the behavior of thePolaris IQ 440 suspension;

FIG. 49 compares the current front ride rate to a target front riderate.

FIG. 50 compares the current center ride rate to a target center riderate

FIG. 51 compares the current rear ride rate to a target rear ride rate.

FIGS. 52-60 show additional rear suspension embodiments of the presentinvention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Features and advantages of the present invention will become apparent tothose skilled in the art upon consideration of the following detaileddescription of illustrative embodiments exemplifying the best mode ofcarrying out the invention as presently perceived.

The embodiments disclosed below are not intended to be exhaustive or tolimit the invention to the precise forms disclosed in the followingdetailed description. Rather, the embodiments are chosen and describedso that others skilled in the art may utilize their teachings.

A progressive rear suspension is disclosed for a rear suspension systemof a snowmobile. A progressive suspension is one having a stiffness thatincreases throughout (or at least substantially throughout) the entirerange of suspension travel.

A diagrammatical depiction of the progressive suspension is shown inFIGS. 8-14, and will be described representatively. This progressivesuspension provides improved ride with less bottoming and better energydissipation.

With reference first to FIGS. 8 and 9, an illustrated embodiment of asuspension 30 of the present invention is shown. Suspension 30 includesa pair of slide rails 12, and a swing arm 31 having a first end coupledto slide rails 12 at location 33 and a second end 35 pivotably coupledto the chassis. A frame 41 (FIG. 9) is configured to define a tunnel 40which receives the track 39 therein. In the illustrated embodiment, themain LFE 32 is located generally horizontally above the tunnel 40 withone end connected to the chassis at location 34 and the other end 36connected to a bell crank 38 that redirects the load vertically. Asecond LFE 37 includes a first end 43 which is pivotably coupled to theslide rails 12. A second end 45 of LFE 37 is pivotably coupled to link47. As shown in FIG. 8, an opposite end of link 47 is pivotably coupledto swing arm 31 by connector 49. As discussed below bell crank 38generally forms a triangular shape with corner 50 coupled to thechassis, corner 52 coupled to end 36 of LFE 32, and corner 54 coupled toend 45 of LFE 37.

It is understood that the actual architecture of the rest of thesuspension 30 may vary from what is shown in FIGS. 8 and 9. Many priorart suspensions may also benefit from this design by connecting thehorizontal LFE 32 to any of the suspension arms through a bell crank 38.The bell crank 32 redirects the shock load vertically. By changing thelength and angles between the input and output arms of the bell crank38, a progressive rate can be achieved for virtually any suspensiondesign.

As discussed above, the main LFE 32 is illustratively placed outside theenvelope defined by track 39 and above the tunnel 40 as shown in FIG. 9.One end 34 of the LFE 32 is connected to the chassis and the other end36 is connected to an end of a bell crank 38. The other end of the bellcrank 38 is connected to the suspension components, either through alink, pivot, slider, or other suitable connection. The suspensioncomponents extend around the track 39 in order to connect componentslocated within the envelope of the track 39 to the LFE 32. Details of anillustrated embodiment of this connection are described below.

As shown in FIG. 9, one such improved suspension places at least one LFEoutside the envelope defined by the track and above the chassis tunnel.One end of the LFE is connected to the chassis and the other end isconnected to an end of a bell crank. The other end of the bell crank isconnected to the suspension components, either through a link, pivot,slider, or other suitable connection. As the suspension compresses intojounce, the suspension end of the bell crank moves vertically someamount which causes the crank to rotate. This, in turn, causes the LFEend of the bell crank to move horizontally and stroke the LFE. This iswhat provides the vertical suspension rate.

Comparing an example of the improved suspension at full rebound (FIG.10) to full jounce (FIG. 11), it is shown that the horizontal distancefrom the crank pivot to the crank suspension end increases. Thisincrease of the “output” bell crank moment arm by itself would make thevertical load decrease through travel. However, the vertical distancebetween the crank pivot and the crank LFE end increases. This increasein the “input” bell crank moment arm balances the increase in the“output” and maintains the vertical load. By changing the relativelength of the arms and the angles between them, a progressive rate canbe generated for most suspension load cases.

The arm lengths and angles of the bell crank 38 are important to theoperation of the suspension 30. FIGS. 10 and 11 show the illustratedembodiment at full rebound and at full jounce, respectively. The largetriangle represents the bell crank 38. The left corner of the triangle50 below the LFE 32 is the pivot connector to the chassis. The top mostcorner 52 is connected to the LFE 32, and the bottom most corner 54 isconnected to the suspension (in this case through the link 47).Comparing the suspension 30 at full rebound (FIG. 1 0) to full jounce(FIG. 11), it is shown that the horizontal distance from the crank pivotto the crank suspension end increases. This increase of the “output”bell crank moment arm by itself would make the vertical load decreasethrough travel. However, the vertical distance between the crank pivotand the crank LFE end increases. This increase in the “input” bell crankmoment arm balances the increase in the “output” and maintains thevertical load. By changing the relative length of the arms and theangles between them, a progressive rate can be generated for mostsuspension load cases.

Another illustrated embodiment uses two bell cranks 42, 44 which connectto the suspension at two points so an LFE 46 is actuated from both endsas shown in FIG. 12. In this illustrated embodiment, the LFE 46 may beplaced front-to-back or left-to-right above the tunnel 40. FIG. 12 showsa design with the LFE 46 placed left-to-right between bell cranks 42,44.

As stated above, the present invention may also be applied to existingrear suspensions, and FIGS. 13 and 14 show a retro-fit to the PolarisFusion® rear suspension shown in FIGS. 1-3. FIG. 13 discloses use of asingle bell crank 38 coupled between rear suspension arm 16 and LFE 32.FIG. 14 discloses use of dual bell cranks 38 and 38′. In FIG. 14, afirst end of bell crank 38 is coupled to end 36 of LFE 32 and a secondend of bell crank 38 is coupled to rear suspension arm 16 by link 51. Asecond bell crank 38′ has a first end coupled to end 34 of LFE 32 and asecond end coupled to front suspension arm 14 by link 51′.

Operation of only one illustrated suspension architecture will bediscussed since the general operation is the same regardless of wherethe suspension end of the bell crank 38 is connected. As the suspensioncompresses into jounce, the suspension end of the bell crank 38 movesvertically some amount which causes the crank 38 to rotate. This, inturn, causes the LFE end of the bell crank 38 to move horizontally andstroke the LFE. This is what provides the vertical suspension rate.

With reference now to FIGS. 15-32, a complete depiction of oneembodiment of the rear suspension 60 of the present invention will bedescribed. Those elements referenced by reference numbers identical tothe numbers above perform the same or similar function.

With reference first to FIG. 15-17, rear suspension 60 is shown attachedto tunnel 40, and illustrates the suspension 60 coupled to a frame 41which defines the tunnel 40 for track 39 (FIGS. 16-17). This system isgenerally comprised of, slide rails 12, LFE 32, bell crank 38, tunnel40, chassis 70, front swing arms 80 and an A-shaped pivot member 96.More particularly, LFE 32 is shown suspended between bell crank 38 and achassis structure 70. Bell crank 38 is attached to A-shaped pivot member96, which in turn is attached to slide rails 12. FIG. 17 shows that themain LFE 32 is located horizontally above the frame 41 which defines thetunnel 40.

In the embodiment of FIGS. 15-17, and as best shown in FIGS. 16 and 17,a front swing arm 80 is pivotably coupled to the slide rails 12 by apivot connection 82 as discussed in further detail below. An oppositeend 84 of swing arm 80 is pivotably coupled to the chassis about which adrive mechanism 85 is attached, having an axis which is coaxial with adrive shaft 86 as also discussed in detail below. With reference firstto FIGS. 18 and 19, the connection of the front swing arm 80 to sliderail 12 will be described.

Traditional suspensions typically mount the front and rear control armsto the slide rails in one of two methods: 1) Pivot shaft extends betweenbeams and passes through a pivot tube on the arm, or 2) A left and rightpivot shaft is mounted to the beams and each pass through a small pivottube on the arm. Although both designs are relatively simple and haveworked well in current designs, there are several problems with both.

The long pivot shaft works well to distribute suspension loads across alarge area on the pivot shaft. However, maintaining lubrication isdifficult and high bending loads can be present thus requiring a largethrough fastener. The short left/right pivot design can be used withsmall self lubricated bushings, but the cantilevered load also requiresa large fastener.

A clevis joint design as shown in FIG. 19 solves the deficiencies ofeach of the above designs. The size of the joint makes it possible touse small lubricated bushings and because the clevis “straddles” therail beam, no bending load is present in the fastener so smallerfasteners may be used with equivalent durability. In this design, theclevis portion of the joint is part of the control arm.

Clevis connection 82 is provided between the swing arm 80 suspensioncomponents and slide rail 12 as shown in FIG. 19. Ends 112 of swing arm80 each include a slot 114 which receives a portion 11 6 of slide rails12 therein. Bolts 118 then secure the ends 112 to portions 11 6 of theslide rails 12.

With respect again to FIG. 18, the front drive mechanism 85 will bedescribed in greater detail. Drive shaft 86 rotates a plurality of drivesprockets 88 which have a plurality of teeth to engage and move thetrack 39 in a conventional manner. A pre-load spring 90 has a first end92 pivotably coupled to swing arm 80 and a second end 93 pivotablycoupled to slide rails 12 at pivot connection 94.

As mentioned above, conventional suspension arrangements pose twoproblems. First, track tension through suspension travel relies on therelative placement of the suspension arms and wheels to the drive shaft.Suspension mount locations are often determined not only by specific,desired suspension characteristics, but on track tension packaging.Problems are encountered from both an over and under tensioning trackstandpoint. Second, the front arm placement is limited to remain outsidethe drive sprocket diameter due to interference with drive traincomponents. This creates problems when attempting to change the weighttransfer behavior of the rear suspension, which is dominated by frontarm mount location.

Both of these problems are solved by mounting the front swing arm 80coaxial with the drive shaft 86 as discussed above and shown in detailin FIG. 18. Because the front swing arm 80 rotates around the same axisas the track drive sprocket 88, track tension is only influenced by theslide rail 12 approach bend profile and the rear suspension idler pulley108. Also, the coaxial placement of the arm 80 creates improved weighttransfer behavior of the rear suspension 60.

There are two illustrated arrangements in which the arm 80 is mountedcoaxial to the drive shaft 86 either on the drive shaft 86 or thechassis. FIG. 18 shows the first arrangement where the arm 80 is mounteddirectly to the drive shaft 86. In this arrangement, bearings are usedin the connection to allow the drive shaft 86 to rotate within the ends84 of the suspension arm 80. The advantages of this connection aretwofold, lateral packaging of the arm 80 in the chassis tunnel iseasier, and the arm strengthens the drive shaft 86. In this embodiment,however, high speed bearings are required at this connection, and thedrive shaft 86 must now react to suspension loads.

The second arrangement for mounting the swing arm 80 is to use largerhollow connections between the suspension arm and the chassis. The driveshaft 86 then passes through this connection. In the illustratedembodiment, a quick change drive shaft assembly is designed to be easilyremoved from a chassis. This provides improved serviceability andmaintenance, and improved assembly procedure.

Traditional snowmobiles have typically used drive shafts that are widerthan the tunnel. This is to simplify the number of parts in the assemblyand still allow mounting to each edge of the tunnel with a single shaft.However, this makes assembly and service difficult. In order to removethe drive shaft you need to open the chain case, loosen the drive shaftbolt, slide the drive shaft out of the chain case, twist the drive shaftand remove it from the tunnel. Sliding the drive shaft and twisting tothe side can be very difficult due to the tunnel/track clearance.

The illustrated embodiment provides two designs that make this processeasier. The first design consists of a two part drive shaft assembly: aninner shaft and outer sleeve. The second consists of a removable splinestub that couples the shaft to the chain case.

This first sleeve embodiment is depicted in FIGS. 20 and 21, andincludes a drive shaft similar to current designs, but the drivesprockets 88 are mounted to an outer sleeve 180 (instead of the shaftdirectly) that is slightly narrower than the tunnel 40. The two partsare then torsionally coupled through either sliding splines, hexes, orother similar fit. The inner shaft 182 is tightly mounted to the chaincase 184 by means of a fastener and the outer sleeve 180 is compressedwhen the inner shaft 182 is tightened from the end opposite the chaincase 184.

To assemble this design, and as best shown in FIG. 21, the sleeve 180 isplaced in the tunnel and the shaft 182 slides completely through thesleeve 180, from the outside of the tunnel, into the chain case 184. Theshaft 182 is torsionally coupled to the drive mechanism inside the chaincase and fastened solidly with a screw 186. The chain case 184 has anaccess opening 187 to install the screw 186 so the case 184 does notneed to be opened to access the drive shaft 182. The entire assembly isclamped tight from the side opposite the chain case 184. As this istightened, the outer sleeve 180 is compressed from each end by the maindrive shaft bearings.

Alternatively, a drive shaft according to FIGS. 22 and 23 could be used,where a spline stub for coupling to the chain case 184 is female insteadof male. This allows the overall length of the shaft 188 and the amountof shaft protruding inside the chain case 184 to be small. A spline stub190 then torsionally couples the shaft 188 to the chain case drivemechanism 192.

To assemble this design, and with reference to FIG. 23, the drive shaft188 is positioned slightly off center from the tunnel, enough for thechain case end of the shaft to clear the tunnel wall. A notch is presentin the tunnel wall for the free end (non-chain case end) of the shaft topass through into the correct position. The drive shaft 188 is thenmoved toward the chain case 184 and pilots on the case bearing. Thespline stub 190 is then inserted from the outside of the chain case 184and torsionally couples the drive shaft 188 to the chain case drivemechanism 192. An access hole 187 is present in the case cover so thecase does not need to be opened to install or remove the stub 190. Afastener 191 is then threadably received in the end of the shaft 188,closest to the case 184, clamping the drive shaft 188 to the chain case.This fastener 191 is then enclosed by a cover 194 for the access hole187. Lastly, the free end of the shaft 188 is tightened against the maindrive shaft bearing.

Both methods are very beneficial with the coaxial mount suspension arm(discussed above). This allows the track and drive shaft to be assembledto the suspension and the entire suspension/track assembly placed intothe chassis all at once.

An important consideration in rear suspension design is maintainingtrack tension through suspension travel. If the track becomes loose, itwill skip drive sprocket teeth and damage the track. Extremely loosetracks can derail. Excessively tight tracks will yield high stresses oncomponents and cause track vibration, stretch, and damage.

Achieving the mount points for desirable rate and kinematics is onlyhalf the challenge of snowmobile suspension design. Packaging a trackaround the suspension is the other. Traditional suspensions sacrificemore optimum suspension geometry to provide track tensioning andpackaging which can be extremely difficult to manage.

The suspension of the present invention packages the suspension aroundthe track. That is, the track actually passes through one or moresuspension components. This design yields superb track tension valuesthroughout travel. Due to a lack of a carrier (upper) track wheel, andcoaxial mounting of the swing arm and drive sprocket, the tension in theillustrated embodiments only relies on the drive sprocket wheel 88 andidler wheels 108 to keep the track tight to prevent “unwrapping” aroundthe rail bend profile as shown in FIGS. 15-17. Track tension is easilytuned by sizing the idler wheel 108 with the drive wheel 88. Therefore,elimination of carrier wheel in conjunction with coaxial swing armmounting greatly simplifies track tensioning in the illustratedembodiments.

With respect now to FIG. 24, A-shaped rear pivot 96 will be described ingreater detail. As mentioned above, A-shaped rear pivot 96 connects bellcrank 38 to LFE 32. A-shaped rear pivot 96 is shown pivotably coupled tobell crank 38 by connection 98. A first arm 100 of pivot 96 is pivotablycoupled to slide rails 12 at location 102. As shown best in FIG. 25,second arm 104 of pivot 96 is coupled to slide rails 12 by a couplingslider 106, having an arced slot 107 that facilitates coupling betweenthe front and rear. A block 105 coupled to arm 104 moves back and forthin slot 107.

This improved suspension also uses a changing “rail link” length tofacilitate coupling. However, the pivot is considerably longer thantraditional due to packaging around and outside the track envelope sothat simple bumpers on the slide rail would not work effectively.Instead, the pivot is shaped as a triangle and the relative anglebetween the pivot and slide rails is limited by a curved slidermechanism, as described with reference to FIG. 25.

The advantages of this system are threefold. First, the horizontallength between the pivot-to-rail mount and the slider can be adjusted toreduce or increase the load within the slider system. Second, the loadbetween these two points is shared by the slide rail itself so noadditional structure is required on the pivot. Third, slots in theslider system provide lateral stiffness to the slide rails so additionalcomponents are not required to increase lateral strength or stiffness.

FIG. 26 shows the attachment of both the rear idlers 108, and a reardeflector 110. Rear idler wheels 108 are coupled to the rear end ofslide rails 12, as best shown in FIG. 26.

All snowmobiles utilize a snow flap to protect the rider and others fromice and snow being thrown from the track. This snow flap is typicallyattached to the chassis behind the rear most wheel of the suspension andis allowed to drag along the ground as the suspension is collapsed.

An alternative design is to use a suspension mounted deflector 1 10similar to a motorcycle fender. By mounting directly to the idler wheelassembly only, the shield moves with the idler wheel when setting tracktension and provides support through the use of an extended arm that isintegral to the wheel assembly.

The following outlines the function of each component in the embodimentshown in FIGS. 15-17. The swing arm 80 is pivotally connected to thechassis coaxial with the drive shaft 86, low and forward on the sliderail 12 to facilitate weight transfer. The pivot 96 is pivotallyconnected to the slide rail 12 near the rear, and to an arced slot 107that facilitates coupling. The pivot 96 is “locked” to the slide rail 12at the extents of the slot 107. The geometry is coupled to the frontwhen the pivot is at the bottom, to the rear when the pivot is at thetop. The crank 38 is pivotally connected to the pivot 96 at one end 54and the chassis at the other end 50. The crank 38 acts as the rear armof the four-link. The preload spring 90 is connected between the swingarm 80 and the slide rail 12. This spring 90 is used for preload biasand does not appreciably affect rate. The main spring/damper 32 isconnected between the crank 38 and the chassis. The location on bothdetermines how progressive the suspension is.

As snowmobiles develop, accommodations in the chassis must be made forfaster, more powerful engines, longer travel suspension, more precisionhandling, and improved durability. This means the chassis must bestronger and stiffer. The most intuitive method to increase strength andstiffness is to directly connect the suspension hard points with moresignificant structure than a thin walled tunnel can provide. The resultis a direct load path between the front suspension mounts, the riderinput points, and the rear suspension mount points, such that the loadpath can only terminate in a structurally durable member of the chassis.

The chassis structure, especially in the rear section of the snowmobile,becomes considerably more important when the LFE reacts outside thesuspension, as described in the above discussion. In this case, rearsuspension loads are not only internal to the suspension, but aredirected into the chassis such that the chassis structure is an integralpart of the suspension. As discussed above, a suspension system isdescribed for support for the LFE 32 above the tunnel 40. The sub frame70 was shown in FIG. 15 for mounting LFE 32 above tunnel 40. Withreference now to FIG. 27, the snowmobile sub frame 70 will be describedfor mounting and supporting the LFE 32 above the tunnel 40.

In the embodiment of FIG. 27, a steering hoop 130 is mounted to oppositesides of the frame 41 (see FIG. 9 and 15) by fasteners 132. Clevisbrackets 134 are provided for coupling to opposite sides of the bellcrank 38 (FIG. 15). A central bracket 136 is provided for coupling toend 34 of LFE 32 (FIG. 15). Four support arms 138 hold the bracket 136in place as best shown in FIG. 27. Support arms 135 extend from brackets134 to brackets 137 on opposite sides of the tunnel frame 41 as shown inFIG. 27. Each arm 135 directs forces along a load path from the bellcrank 38 along a line 139 (shown in FIG. 15 and 28) which passes throughthe axis or rotation of the drive shaft 86. FIG. 28 illustrates that aplurality of load paths are directed through the axis of rotation ofdrive shaft 86.

In another illustrated embodiment shown in FIGS. 29 and 30, a sub frameassembly 140 connects the two rear suspension pivots 142, 144 and thetop of the steer hoop 146. The sub frame 140 provides much moretorsional stiffness than traditional stressed tunnel systems.

A traditional snowmobile chassis relies solely on the tunnel frameassembly 41 to provide support for the rear suspension. Modernperformance snowmobiles are reaching levels of performance at which astiffer chassis would be ideal. By using a frame to attach directly tothe pivot points of the suspension, and tie into existing structurefound at the steering hoop 146, the support structure of the rearsuspension is made much stiffer. The tunnel frame 41, while still partlysupporting the rear suspension, is primarily acting as a track shieldand foot support.

The sub frame 140 includes 5 major points of connection to thesnowmobile: The front and rear axis created by the rear suspension (onboth sides of the snowmobile), and the top of the steer hoop, which willattach to existing structure in the front of the snowmobile. Connectionsat the suspension axes allow actual suspension pivots (shafts, bolts,etc.) to pass through the sub frame 140. The frame also has means (suchas flanges) to attach to the tunnel frame 41.

The sub frame 140 sits atop the tunnel frame 41 as shown in FIG. 30 andis fastened to the tunnel frame 41, suspension pivots 142,144 and steerhoop 146. As rear suspension pivots are attached directly to the frame,no load is transferred between the suspension and sub frame through thetunnel frame 41.

Steer hoop 146 is coupled to rear suspension pivots connectors 142 byarms 148. The top of steer hoop 146 is also coupled to the rearsuspension pivot connectors 142 by an arm 150 connected to U-shapedmember 152.

An advantage of this structure is the direct load paths between the LFEmount, the rear arm mount, and the front arm mount. Because the frontarm is mounted coaxial with the driveshaft, the drivetrain (such asgearcase or transmission) also needs to be structural and becomes anintegral part of the chassis structure. With this system, the tunnelitself may or may not be important to the overall chassis strength. Ifthe tunnel was not structural, it would only acts as a snow shield andfoot support.

This rear chassis structure, in particular, may be removable and form atype of chassis substructure or subframe, as shown in FIG. 15 and 30.The sub frame includes four major points of connection to thesnowmobile: the front and rear arm mounts of the rear suspension, theLFE mount, and the steering hoop, which is attached to structure in thefront of the snowmobile.

The subframe also makes for a logical attachment for a snowmobile seat.By integrating a type of seat frame into this structure, as shown inFIGS. 31 and 32, rider input is also more efficiently directed into thedurable portion of the rear structure. In the embodiment of FIGS. 31 and32, a snowmobile seat includes a mounting frame 161 supported by theexisting structure of sub frame 160. A seat bun 168 attaches to thisframe 161.

With reference still to FIGS. 31 and 32, a U-shaped arm 162 has oppositeends coupled to rear suspension pivot connectors 142 so that theU-shaped arm 162 extends upwardly above the tunnel 41 as shown in FIG.32. First and second seat mount frame arms 164 and 166 extend betweenthe U-shaped arm 162 and arm 150. A seat bun 168 is then coupled to arms164 and 166. This structure provides an open region 170 below seat bun168 for storage.

FIGS. 33 and 34 show an alternative embodiment of a seat mount frame 172mounted to an existing tunnel frame 41 by welding or suitable fasteners.This embodiment provides an open region 174 beneath a seat bun 176 asshown in FIG. 34.

Modern snowmobile seats rely on a plastic bun to attach to thesnowmobile, often using the gas tank to help add support to the seat.This restricts under seat room, limits how thin a seat can be, andrelies on plastic to hold up to loads created by a rider. The seat bungeometry is constrained to be adequately strong, limiting how narrow itcan be. A two piece mounting system would prove stronger, allow moreroom, and could be thinner.

Regardless of means of attachment, the seat mount frame transmits loadfrom rider to existing chassis structure. The primary function of theseat bun is to secure the seat padding and cover to the mount frame,where as modern plastic seat buns also transmit load to the chassis.

The illustrated design features of the architecture of the rearsuspension disclosed herein are summarized as follows: the main shockand damper (LFE 32) are mounted above the track 39 and above the tunnel40 and react on the chassis. The chassis structure disclosed withreference to 27-32 facilitate the over tunnel LFE design. At least onesuspension arm mounts to the chassis above the track, and the trackpasses through at least one suspension component. In other words, atleast one component “wraps” around the track. The suspension 60 does nothave a carrier wheel which yields a triangular track wrap path. Slidersand bumpers are used to control the track direction, but these are notnormally in contact with the track. Swing arm 80 mounts to the chassiscoaxial with the drive shaft 86. Track 39 and drive shaft 86 are part ofthe suspension subsystem. They are installed and removed from thevehicle as one unit. A slider slot 107 is used to control the relativeangle of the pivot 96 to the slide rail 12 as shown in FIG. 24. A block105 coupled to arm 104 moves back and forth in slot 107. This controlsboth front-to-rear and rear-to-front coupling. More simple bumpers maybe used on the slide rail instead of a slot 107, but the slot 107 offerslateral and longitudinal stiffness. A deflector shield 110 is mounted toidler wheel assembly 108 as shown in FIGS. 18 and 25. By mountingdirectly to this assembly only, the shield 110 moves with the idlerwheel 108 when setting track tension. The vertical difference betweenthe front and rear arm chassis mounts is illustratively 20% or more ofthe chassis link length (D). Finally, A/B ratio of links A and B isillustratively 1.6 to 2.0 or greater.

FIG. 35 diagrammatically illustrates the four-link geometry of theembodiment of FIGS. 15-17 as compared to FIG. 1. FIGS. 36 and 37illustrate the coupled behavior, under front and rear loadsrespectively.

FIGS. 38 and 39 compare the load vs. deflection of a conventionalsuspension (illustratively the Polaris IQ 440 suspension) to thesuspension system of the present improved suspension. Note how the frontload case shown in FIG. 38 is inversely proportional to the frontcoupling angle shown in FIG. 7. Therefore, rear rate is not dependant oncoupling when: 1) front rate is only dependant on front coupling, and 2)rear LFE reacts only on rear arm.

The advantage of a progressive suspension is improved ride quality withimproved energy absorption, or less bottoming. A progressive suspensioncan be setup to have a very low stiffness at the vehicle ride height toprovide very little input to the chassis and rider over small bumps andstill provide bottom-out resistance over large bumps due to the increasein rate near full jounce. This can best be visualized by the area underthe force/deflection curve (energy) in FIG. 40. The energy absorbed nearride is very low on a progressive suspension but is very high at fulljounce. Also note that a regressive suspension still shows an increasein load but the rate (slope of the load curve) is decreasing at fulljounce as shown in FIG. 40.

A snowmobile suspension is different from any other vehicle becausethere is a vertical stiffness associated with the front of the tracksuspension, the center of the track suspension, and the rear of thetrack suspension. This means that even though there is only onesuspension architecture, all three rates need to be managed. The designsof the present invention yield progressive rates in all three loadcases, and is shown in FIG. 41.

FIGS. 42-44 are computer simulations of movement of the progressive rearsuspension of the present invention. The top views shown in FIGS. 42-44illustrate the suspension in a front load case, and the bottom viewshows the suspension in a rear load case. FIG. 42 illustrates thesuspensions in full rebound. FIG. 43 illustrates the suspensions atapproximately half way through the range of movement of the suspensionsduring load applications. FIG. 44 illustrates the front load case andthe rear load case at full jounce.

FIGS. 45-48 are plots characterizing the general behavior of thesuspension of the present invention, compared to the behavior of abenchmark suspension which is illustratively the Polaris IQ 440suspension. In the plots, the Polaris IQ 440 suspension is listed as the“Racer” suspension and the suspension of the present invention islabeled the “Improved” suspension.

FIG. 49 compares the current front ride rate to a target front riderate. Front ride rate is currently regressive. An ideal target curve is“softer” but more progressive as shown in FIG. 49. Front ride rate curveis also preferably less than center rate.

FIG. 50 compares the current center ride rate to a target center riderate. Current suspensions have a center ride rate which is slightlyregressive. A slightly more progressive rate would be much better asshown by the target rate.

FIG. 51 compares the current rear ride rate to a target rear ride rate.Rear rate needs to most work. When coupled, the suspension over centers.When uncoupled, the suspension transfers excessively but shows goodrate. Preferably, rear bias should be higher than center bias.

Additional rear suspension embodiments of the present invention areillustrated in FIGS. 52-60. Each embodiment has certain merits that areunique.

The majority of the following concepts utilize a long swing arm whichhas been determined to yield poor traction and weight transfer. However,the topology of the remaining architecture yields desirable rate andcoupling behavior. In particular, all utilize a shock above thesuspension mounted to the chassis actuated with a bell crank.

Each discussion has four parts: Background, Drawbacks, Architecture,Front Coupling, and Rear Coupling. The last three are the metrics thatwere tracked during the design process. The last metric, Traction, ismore of a dynamic metric that is not easily described or realized fromthese pictures.

A snowmobile rear suspension requires at least 2 points mounted tochassis, and at least 2 points mounted to the rails. The in-betweenlinkage is the novelty between one suspension and the next. Most of theembodiments with the long arm form a type of “X” linkage, the latershorter arm concepts look more like a traditional 4 link.

Embodiments of FIGS. 52 and 53 Background

FIG. 52 illustrates a “over tunnel” shock mount design. FIG. 53illustrates is variation of the FIG. 52 embodiment where the couplingmechanism is mounted, but the basic function is similar. This was donefor packaging concerns around the track.

Architecture

Swing arm mounts to the chassis at one end, the slide rail at the other.

Pivot mounts to the swing arm at one end and the crank at the other.

Crank mounts to the pivot at one end, the chassis at the other, and theshock.

Coupling mechanism is a linear slider with bump stops and mounts to theslide rails at one end and the crank at the other.

Front Coupling

As the front of the rail is loaded, the coupling mechanism (slider) isalready at its shortest position. The load is transferred up thismechanism and forces the crank to start rotating CCW. The pivot pullsthe swing arm upward which in turn pulls the rear of the rail upwardthus coupling the rear of the beam to the front.

Rear Coupling

As the rear of the rail is loaded, the swing arm moves upward. The pivotrotates CW, the crank rotates CCW. The coupling mechanism extends to apreset point which then pulls the front of the slide rail upward thuscoupling the front of the rail to the rear.

FIG. 55 illustrates an embodiment with “decoupling” of the front andrear coupling mechanism. Front coupling may be tuned independently ofrear coupling and the rear coupling stiffness may be tuned with aspring/shock. It also packaged around the track very well.

Architecture

Swing arm mounts to the chassis at one end, the slide rail at the other.

Pivot mounts to the swing arm at one end with a slider/revolute, and thecrank at the other.

Crank mounts to the pivot at one end, the chassis at the other, and theshock.

Drop link mounts between the pivot and slide rails.

Front coupling block limits the forward sliding motion between the pivotand swing arm.

Rear coupling shock mounts between the pivot and the slide rail andlimits the rearward sliding motion between the pivot and the swing armonce fully compressed.

Front Coupling

As the front of the rail is loaded, the drop link forces the pivot slideup on the swing arm. However, the front coupling block limits thismotion which forces the pivot to rotate CW. The pivot pulls the swingarm upward which in turn pulls the rear of the rail upward thus couplingthe rear of the beam to the front.

Rear Coupling

As the rear of the rail is loaded, the swing arm moves upward. The pivotslides rearward until the rear coupling shock is fully compressed. Thepivot is then forced to rotate CW which pulls the drop link and railupward thus coupling the front of the rail to the rear.

FIG. 55 illustrates an embodiment to reduce the complexity of theembodiment of FIG. 54. The slider between the pivot and swing arm iseliminated and the loads were reduced slightly due to alternativecoupling mechanisms. Front and rear coupling may be adjustedindependently and rear coupling stiffness are adjustable. The front/rearcoupling mechanism is separate.

Architecture

Swing arm mounts to the chassis at one end, the slide rail at the other.

Pivot mounts to the swing arm at one end and the crank at the other.

Crank mounts to the pivot at one end, the chassis at the other, and theshock.

Front coupling slider between the slide rail and pivot.

Rear coupling shock mounts between the front coupling slider structureand the pivot.

Front Coupling

As the front of the rail is loaded, the front coupling slider is alreadycompressed completely. This forces the pivot to rotate CW and the crankCCW. The pivot pulls the swing arm upward which in turn pulls the rearof the rail upward thus coupling the rear of the beam to the front.

Rear Coupling

As the rear of the rail is loaded, the swing arm moves upward. The pivotrotates CW until the rear coupling shock is fully extended. The pivot isthen forced to rotate CW which pulls the rail upward thus coupling thefront of the rail to the rear.

FIG. 56 illustrates design having a short swing arm for improvedtraction. In many ways it looks very traditional—the shock mountedbetween the two arms, bumper type coupling blocks, rear arm mounted tothe pivot, etc. The main difference was pushing the upper rear arm mounthigh in the chassis and mounting the rear shock mount high as well.

Architecture

Swing arm mounts to the chassis at one end, the front of the slide railat the other.

Rear arm mount to the chassis at one end, the pivot at the other.

Pivot mounts to the rear arm at one end the rear of the rail at theother.

Pivot deflection is limited by bumpers on the rail beam.

Shock is mounted to the rear arm at one end, shock pivot at the other.

Shock pull rod is mounted to the rear arm at one end, the shock pivot atthe other.

Front Coupling

As the front of the rail is loaded, the pivot rotates forward until itcontacts the front coupling block. This locks the suspension into a fourlink geometry and couples the rear of the rail to the front.

Rear Coupling

As the rear of the rail is loaded, the pivot rotates rearward until itcontacts the rear coupling block. This locks the suspension into a new,unique four link geometry and couples the front of the rail to the rear.

FIG. 57 illustrates a “shock over tunnel” design with a short swing arm.The coupling mechanism is similar to that of FIG. 53. FIG. 58illustrates a refinement of FIG. 57 embodiment which places the couplinglink more vertical to reduce loads.

Architecture

Swing arm mounts to the chassis at one end, the front of the slide railat the other.

Pivot mounts to the crank at one end the rear of the rail at the other.

Crank is mounted to the chassis at one end, the pivot at the other.

The shock is mounted between the chassis and the crank.

The coupling link is a slider linkage that is mounted between the pivot(crank on FIG. 58) and the swing arm. This linkage limits the rotationof the pivot.

Front Coupling

As the front of the rail is loaded, the pivot rotates forward until thecoupling link is fully compressed. This locks the suspension into a fourlink geometry and couples the rear of the rail to the front.

Rear Coupling

As the rear of the rail is loaded, the pivot rotates rearward until thecoupling linkage is fully extended. This locks the suspension into anew, unique four link geometry and couples the front of the rail to therear.

FIG. 59 illustrates a design similar to the embodiment described above.The coupling linkage is eliminated in favor of bumpers on the rail thatlimit the pivot rotation. FIG. 60 illustrates an embodiment similar toFIG. 59 but the limiting occurs between the pivot and crank.

Architecture

Swing arm mounts to the chassis at one end, the front of the slide railat the other.

Pivot mounts to the crank at one end the rear of the rail at the other.

Crank is mounted to the chassis at one end, the pivot at the other.

The shock is mounted between the chassis and the crank.

Bumpers on the rail limit the rotation of the pivot (FIG. 59).

Slider/bumpers between the pivot and crank limit the rotation of thepivot (FIG. 60).

Front Coupling

As the front of the rail is loaded, the pivot rotates forward until itcontacts the front bumper. This locks the suspension into a four linkgeometry and couples the rear of the rail to the front.

Rear Coupling

As the rear of the rail is loaded, the pivot rotates rearward until itcontacts the rear bumper. This locks the suspension into a new, uniquefour link geometry and couples the front of the rail to the rear.

While this invention has been described with reference to exemplarydesigns, the present invention may be further modified within the spiritand scope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains.

While this invention has been described as having an exemplary design,the present invention may be further modified within the spirit andscope of this disclosure. This application is therefore intended tocover any variations, uses, or adaptations of the invention using itsgeneral principles. Further, this application is intended to cover suchdepartures from the present disclosure as come within known or customarypractice in the art to which this invention pertains.

1. A snowmobile suspension system, comprising: a frame; slide rails for mounting endless track; at least one linkage between the slide rails and frame, the linkage comprising a pivot link, where the pivot link pivots in response to movement between the slide rails and the frame; and at least one linear force element (LFE) positioned between the pivot link and the frame, whereby pivotal movement of the pivot link strokes the LFE.
 2. The snowmobile suspension system of claim 1, wherein the at least one LFE is positioned above the frame.
 3. The snowmobile suspension system of claim 2, wherein the at least LFE is substantially horizontal throughout its movement.
 4. The snowmobile suspension system of claim 1, wherein the at least one linkage is positioned adjacent to a rear of the slide rails and defines a rear suspension system.
 5. The snowmobile suspension system of claim 4, wherein the pivot link is comprised of a bell crank, which connects to one end of the LFE.
 6. The snowmobile suspension system of claim 5, wherein the linkage is further comprised of a rear suspension frame operatively linked to the slide rails and the bell crank.
 7. The snowmobile suspension system of claim 6, wherein the rear suspension frame is comprised of straddle links, which flank the endless track.
 8. The snowmobile suspension system of claim 7, wherein the straddle links are defined as A-shaped links, having plural attachments to the slide rails and a single upper pivot link.
 9. The snowmobile suspension system of claim 5, wherein the bell crank is pyramidally shaped, with front corners attached to the frame, rear corners operatively connected to the slide rails, and the apex attached to the LFE.
 10. A snowmobile suspension system, comprising: a frame; slide rails for mounting endless track; at least one linkage between the slide rails and frame; and at least one linear force element (LFE) positioned above the frame and operatively connected to the frame and to the at least one linkage.
 11. The snowmobile suspension system of claim 10, wherein the at least one linkage is positioned adjacent to a rear of the slide rails and defines a rear suspension system.
 12. The snowmobile suspension system of claim 11, wherein the linkage is comprised of a bell crank, which connects to one end of the LFE.
 13. The snowmobile suspension system of claim 12, wherein the wherein the linkage is further comprised of a rear suspension frame operatively linked to the slide rails and the bell crank.
 14. The snowmobile suspension system of claim 13, wherein the rear suspension frame is comprised of straddle links, which flank the endless track.
 15. The snowmobile suspension system of claim 14, wherein the straddle links are defined as A-shaped links, having plural attachments to the slide rails and a single upper pivot link.
 16. The snowmobile suspension system of claim 15, wherein the bell crank is pyramidally shaped, with front corners attached to the frame, rear corners operatively connected to the slide rails, and the apex attached to the LFE.
 17. A snowmobile suspension system, comprising: a frame; slide rails for mounting endless track; at least one linkage between the slide rails and frame; and at least one linear force element (LFE) positioned substantially horizontally, with one end attached to the frame and one end connected to the at least one linkage.
 18. The snowmobile suspension system of claim 17, wherein the at least LFE is positioned above the frame.
 19. The snowmobile suspension system of claim 17, wherein the at least one LFE is substantially horizontal throughout its movement.
 20. The snowmobile suspension system of claim 17, wherein the linkage is comprised of a pivot link which pivots in response to movement between the slide rails and the frame, and LFE is positioned between the pivot link and the frame, whereby pivotal movement of the pivot link strokes the LFE.
 21. The snowmobile suspension system of claim 17, wherein the at least one linkage is positioned adjacent to a rear of the slide rails and defines a rear suspension system.
 22. The snowmobile suspension system of claim 21, wherein the pivot link is comprised of a bell crank, which connects to one end of the LFE.
 23. The snowmobile suspension system of claim 22, wherein the linkage is comprised of a rear suspension frame operatively linked to the slide rails and the bell crank.
 24. The snowmobile suspension system of claim 23, wherein the rear suspension frame is comprised of straddle links, which flank the endless track.
 25. The snowmobile suspension system of claim 24, wherein the straddle links are defined as A-shaped links, having plural attachments to the slide rails and a single upper pivot link.
 26. The snowmobile suspension system of claim 23, wherein the bell crank is pyramidally shaped, with front corners attached to the frame, rear corners operatively connected to the slide rails, and the apex attached to the LFE.
 27. A snowmobile suspension system, comprising: a frame; slide rails coupled to the frame; endless track mounted to the slide rail; at least one linear force element (LFE) positioned outside of the envelope defined by the endless track; a suspension assembly coupling the slide rails to the frame; whereby one end of the LFE is attached to the frame and the opposite end is attached to the suspension assembly, with the endless track passing through the suspension assembly.
 28. The snowmobile suspension system of claim 27, wherein the at least one LFE is positioned above the frame.
 29. The snowmobile suspension system of claim 27, wherein the at least one LFE is substantially horizontal throughout its movement.
 30. The snowmobile suspension system of claim 27, wherein the suspension assembly is comprised of a pivot link which pivots in response to movement between the slide rails and the frame, and LFE is positioned between the pivot link and the frame, whereby pivotal movement of the pivot link strokes the LFE.
 31. The snowmobile suspension system of claim 30, wherein the pivot link is comprised of a bell crank, which connects to one end of the LFE.
 32. The snowmobile suspension system of claim 27, wherein the suspension assembly is comprised of straddle links, which flank the endless track.
 33. The snowmobile suspension system of claim 32, wherein the straddle links are defined as A-shaped links, having plural attachments to the slide rails and a single upper pivot link.
 34. The snowmobile suspension system of claim 31, wherein the bell crank is pyramidally shaped, with front corners attached to the frame, rear corners operatively connected to the slide rails, and the apex attached to the LFE.
 35. A snowmobile suspension system, comprising: a frame; slide rails for mounting endless track; a suspension system mounted intermediate the frame and the slide rails, the suspension stiffness increasing at least substantially throughout the entire range of suspension travel.
 36. The snowmobile suspension system of claim 35, wherein the suspension system is comprised of at least one linear force element (LFE) positioned outside of the envelope defined by the endless track and a suspension assembly coupling the slide rails to the frame; whereby one end of the LFE is attached to the frame and the opposite end is attached to the suspension assembly, with the endless track passing through the suspension assembly.
 37. The snowmobile suspension system of claim 36, wherein the at least one LFE is positioned above the frame.
 38. The snowmobile suspension system of claim 36, wherein the suspension assembly is comprised of a pivot link which pivots in response to movement between the slide rails and the frame, and the LFE is positioned between the pivot link and the frame, whereby pivotal movement of the pivot link strokes the LFE.
 39. The snowmobile suspension system of claim 38, wherein the pivot link is comprised of a bell crank, which connects to one end of the LFE.
 40. The snowmobile suspension system of claim 39, wherein the suspension assembly is comprised of straddle links, which flank the endless track.
 41. The snowmobile suspension system of claim 35, wherein the suspension system is comprised of forward links operatively coupled adjacent to a front of the slide rails having an effective length (A); rearward links operatively coupled adjacent to a rear of the slide rails having an effective length (B); and at least one linear force element (LFE) positioned intermediate the rearward links and the frame.
 42. The snowmobile suspension system of claim 41, wherein the ratio of the links (A/B) is between 1.6 to 2.0. 